Wind is one of the most active forces shaping Mars’ surface in today’s climate. The wind has carved the features we call “yardangs,” one of many in this scene, and deposited sand on the floor of shallow channels between them. On the sand, the wind forms ripples and small dunes. In Mars’ thin atmosphere, light is not scattered much, so theandnbsp;shadows cast by the yardangs are sharp and dark.

Running across the image center is one the largest canyons in the Solar System. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth’s Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Several geologic processes have been identified in the canyon. The featured mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s.